In or relating to crawlers

ABSTRACT

A dual-mode crawler unit for traversing a generally tubular target, the unit comprising means for effecting a hand-over-hand action along the target and also means for effecting a driven action along the target, the unit comprising two or more traversing units, the units being directly connected to each other by one or more linear actuators.

FIELD OF THE INVENTION

The present invention relates generally to crawlers, climbers and the like for traversing a generally tubular target such as an umbilical, riser or pipe.

BACKGROUND

There are already in existence umbilical, riser or pipe climbers, which use either a hand-over-hand climbing operation, or a set of driven rollers to propel itself along the length of the umbilical, riser or pipe.

Hand-over-hand movement is done by extending an open clamp in the direction of travel, while a trailing clamp remains clamped to the umbilical, riser or pipe. Once extended the leading clamp is closed onto the umbilical, riser or pipe to grip it, before opening the trailing clamp and retracting it towards the previously extended leading clamp. This method of propelling the unit, while versatile, can be a slow stop-start action.

Using a set of driven wheels or tracks clamped onto the umbilical, riser or tube for traction gives a smoother, faster, and continues way of propelling the climber unit. The problem with using only driven tracks or rollers for propulsion is that it does not lend itself to allowing the crawler unit to pass items (such a strakes or buoyancy) or anything that deviates too much from a continuous uniform diameter.

According to an aspect of the present invention there is provided a dual-mode crawler unit for traversing a generally tubular target, the unit comprising means for effecting a hand-over-hand action along the target and also means for effecting a driven action along the target, the unit comprising two or more traversing units, the units being directly connected by one or more linear actuators.

In some embodiments two traversing units are provided and are connected to each by one or more linear actuators. In embodiments with more than two traversing units, they are connected to each other by respective linear actuator/s.

The linear actuator may comprise a non-jointed actuator (linear actuation is achieved with no rotation).

The traversing action may be of the “push me pull you” type.

The target may be a riser or umbilical.

Conduits to transfer materials from the seafloor to production and drilling facilities atop the water's surface, as well as from the facility to the seafloor, subsea risers are a type of pipeline developed for this type of vertical transportation. Whether serving as production or import/export vehicles, risers are the connection between the subsea (oil) field developments and production and drilling facilities. Similar to pipelines or flowlines, risers transport produced hydrocarbons, as well as production materials, such as injection fluids, control fluids and gas lift. Usually insulated to withstand seafloor temperatures, risers can be either rigid or flexible.

Umbilicals play an important role in offshore and subsea oil and gas developments. They provide the connection between the host facility through which control is exercised, power transmitted and utilities such as injection chemicals delivered to subsea wells. Current trends in the market—the growing number of satellite developments from mature fields, the advance of exploration and production into ever deeper waters and the increasing length of step-outs—indicate that in coming years umbilicals will play an even more important role in offshore oil and gas production.

Umbilicals are long flexible constructions made up of tubes, cables, armouring, fillers and wrapping contained with a protective sheath. The most common form of umbilical often contains electric cables for transmitting control and power signals, and high-, medium- or low-pressure tubes for carrying hydraulic liquids to control valves and chemicals for injection into the well or pipeline. It is therefore known as an electro-hydraulic umbilical. There may be additional elements—for example, fibre-optic cables for monitoring purposes are increasingly being incorporated.

A further aspect provides a subsea bi-directional tool for traversing a generally tubular target, in which the tool includes means for monitoring and correcting rotational position, comprising a sensor for providing absolute or relative rotation to a target and means for actively rotating the unit.

According to a further aspect of the present invention there is provided a dual-mode crawler/climber unit for traversing a generally tubular target, the unit comprising means for effecting a hand-over-hand action along the target and also means for effecting a driven action along the target.

The present invention also provides a subsea bi-directional tool for traversing a generally tubular target, the unit comprising means for effecting a hand-over-hand action along the target and also means for effecting a driven action along the target.

The tubular target may be, for example, an umbilical, riser or pipe.

In units or tools provided by the present invention the means for effecting a driven action may be incorporated into the means for effecting a hand-over-hand action.

The means for effecting a driven action may comprise rollers, tracks, wheels, bristle drive or the like.

The means for effecting a hand-over-hand action may comprise two or more clamps.

The clamps may be capable of moving toward and away from each other along the target.

There may be two sets of driven rollers, tracks or wheels separated by a linear actuator, and in which each set of driven rollers or tracks is capable of supporting and propelling the unit/tool along the target without the other being in contact with the target.

There may be a set of driven rollers, tracks or wheels capable of supporting and propelling the crawler along the umbilical, riser or tube, separated by a linear actuator from a set of rollers capable of rotating the crawler about the umbilical, riser or tube axis.

There may be a set of driven rollers or tracks separated from a clamp by a linear actuator.

The means for effecting a driven action and/or the means for effecting a hand-over-hand action may be retractable.

The means for effecting a driven action and/or the means for effecting a hand-over-hand action may be retractable.

The means for effecting a drive action may be movable between a retracted position and an engaged position. For example, in a system with two or more positions of driving engagement it may be possible to lock a set (for example a set of wheels) to prevent rotation whilst a hand-over-hand action is being effected (for example while an upstream/downstream clamp is released).

Units or tools may include thrusters for traversing the target and/or for keeping the unit/tool concentric with the target during movement.

Units or tools may include sensors for keeping the unit/tool concentric with the target.

The unit or tool may include the capability to adjust clockwise or anticlockwise rotation bias. For example, it may include the capability to adjust the trim of a roller, track or wheel in contact with the target to cause the unit/tool to rotate about the target.

Units or tools may incorporate a sensor for giving its rotational position, either absolute, or relative to a datum.

A control system may be used to automatically adjust clockwise or anticlockwise bias to maintain a desired rotational position or path on the target.

The control system may be a programmable logic controller (PLC).

The means for effecting hand-over-hand action may comprise clamps and the clamps may include a set of overlapping fingers forming an aperture which retain the target when the clamps are opened, and centralise the target as the clamps are closed.

Units or tools may include an on-board electrically driven HPU. Electrical power may be provided via an umbilical or cable from a power supply remote to the unit/tool.

The on-board HPU may be used to supply hydraulic fluid to motors and/or cylinders and/or additional on-board systems.

The unit or tool may include a module for cleaning the target. The module may clean the target, for example, by scraping and/or rotating brushes and/or water jetting.

The unit or tool may include a sensor or inspection module.

In embodiments with cleaning and sensor modules the sensor module may be positioned “after” (i.e. downstream) the cleaning module.

The unit or tool may include a set of subsea thrusters to enable the crawler unit/tool to swim, so to position itself around the target when in water.

The position of centre of gravity and centre of buoyancy of the unit/tool may be in or near to the same position.

The present invention also provides a method of traversing a tubular target as described herein.

In some aspects and embodiments the invention is the use of at least a single set of driven rollers or tracks alongside a crawling type method of propulsion. By combing these two methods of propulsion the crawling unit is able to propel itself along an umbilical, riser or pipe in a continues manner at reasonable speed, while still being able to crawl along sections where it is not possible to use driven wheels or tracks, such as when clearing an object such as a strake or buoyancy.

The unit may also be able to ‘step over’ obstacles in some embodiments, by retracting its driven rollers or tracks approaching an obstacle, and using an additional trailing set of driven rollers or tracks to move the leading retracted set over the obstacle.

This method of stepping over an obstacle may be further enhanced with the individual sets of rollers capable of extending away, and retracting back toward each other, as by moving further apart allows the crawler unit to ‘step over’ a larger gap.

Once the leading set of rollers or tracks has moved beyond an obstacle, they re-clamp to the umbilical, riser or pipe, and the trailing set are retracted.

The leading set of driven rollers or tracks is then used to move the trailing retracted set over the obstacle, so moving the entire unit beyond the obstacle.

Another aspect of the present invention relates to the monitoring and correction of the crawling unit rotational position. As the unit moves along the umbilical, riser, or tube it may undergo multiple revolutions, hampering the management of the connecting power and control umbilical, as it could be being wrapped around the umbilical, riser, or tube the unit it is traversing.

The invention is to use a sensor, such as a magnetometer or gyroscopic compass, to give the absolute or relative rotation to the umbilical, riser, or tube. By knowing the number of rotations, and in which direction, the crawler unit has gone through, the unit can be actively rotated to reduce or remove the number times which the power umbilical has been wound around the umbilical, riser, or tube.

One embodiment of this could simply involve adjusting a clockwise/anticlockwise bias, which could be done by adjusting the angle of a contacting passive or driven roller. Either an operator could manually adjust this as the unit traverses, or it could be used in conjunction with a control system to continually adjust the bias to prevent the crawler unit going through any rotation.

Rather than introduce a clockwise or anticlockwise bias as the unit transverses along the umbilical, riser or tube, the unit could be stopped, and then rotated about the axis of the umbilical, riser or tube using a set of rollers.

These rollers could either be fixed, with sole purpose of rotating the crawler unit about the umbilical, riser, or tube axis, or they could be the same rollers used for traversing rotated through or near to 90 degrees (pivoted about axis perpendicular to umbilical, riser or tube axis).

Another innovation is the incorporation of a set of overlapping fingers forming an aperture, which are required to both position the umbilical, riser or tube as the clamping mechanism is closed, and to fully encompass the umbilical, riser or tube when the clamps are open.

The detail of these fingers is better described in the following embodiments; however, the fundamental invention is the incorporation of a method or mechanism to centralise the umbilical, riser or tube within the clamping elements.

The crawler unit is intended to deliver either cleaning tools, Inspection equipment, or both. However, the crawler unit described in the preferred embodiment could well be used to move other modular subsea equipment packages along an umbilical, riser or tube.

In some embodiments the present invention relates to a riser cleaning and inspection robot.

In some embodiments the present invention relates to a riser and umbilical crawler. The purpose of the may be to remove marine fouling, and to position a flexible inspection tool along an umbilical or riser. The crawler unit may be capable of both foul removal and inspection tool deployment.

The crawler may, for example, be a subsea vehicle.

A further aspect provides a crawler unit comprising a frame with a generally central roller set, a pair of lateral roller sets being provided on or by opposite sides of the frame and being movable from an open position in which the frame can be positioned on a tubular target with the central roller set engaged, and a closed position in which the lateral roller sets are closed around the target and engage thereon.

The central and/or lateral roller sets may comprise one or more rollers. In some embodiments the rollers are concave.

In some embodiments all rollers are driven. In other embodiments some rollers are passive. For example the central roller set (including one or more rollers) may be passive and the or one of the rollers on either or both of the arms may be driven, for example by a direct drive hydraulic motor.

In some embodiments front and rear arm pairs are provided at or towards either end of the frame and close around the target. The lateral roller sets may be positioned between the front and rear arms.

Different aspects of the present invention may be used separately or together.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the independent and dependent claims may be combined with the features of the other independent and dependent claims as appropriate, and in combination other than those explicitly set out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a crawler unit formed according to an embodiment of the present invention;

FIG. 2 shows end views of the unit of FIG. 1 with: i) a clamp closed and guides closed; ii) a clamp closed and guides closed for a smaller diameter target; and iii) a clamp closed and guides open;

FIG. 3 is a magnified view showing different positions of clamping and centralising units;

FIG. 4 shows the unit of FIG. 1 in use, driving along a tubular target until it meets an obstruction;

FIG. 5 shows the unit of FIG. 4 rotated to align a gap with a mooring line;

FIG. 6 shows the crawling unit front module extending in a direction of travel towards the obstruction;

FIG. 7 shows the rear module being retracted towards the front module;

FIG. 8 shows the front module again being extended so as to pass over the obstruction;

FIG. 9 shows the unit following repeated cycles of front module extension/rear module retraction hand-over-hand propulsion process;

FIG. 10 shows a bidirectional tool formed according to a further embodiment;

FIG. 11 shows an end view of the tool of FIG. 10;

FIG. 12 shows the tool in an open position whilst being affixed to a tubular structure.

FIG. 13 illustrates a centraliser finger closing sequence for the tool;

FIG. 14 shows the tool of FIG. 10 in a swimming mode;

FIGS. 15 to 18 illustrate the tool stepping over an obstacle;

FIGS. 19 to 24 illustrate the tool negotiating multiple objects;

FIG. 25 shows a crawling module of a unit formed according to a further embodiment;

FIG. 26 shows the module of FIG. 25 together with a cleaning module;

FIG. 27A shows the unit open and positioned around a 14 inch diameter umbilical;

FIG. 27B shows the unit closed around the umbilical;

FIG. 27C shows the unit closed around an 8 inch umbilical;

FIG. 28 illustrates the tool being positioned amongst tightly packed umbilicals;

FIG. 29 shows the unit with an inspection tool attached;

FIG. 30 shows a possible system architecture for operating the unit;

FIG. 31 shows the unit attached to an umbilical; and

FIG. 32 in an end view showing the unit of FIG. 21 attached around an umbilical.

DETAILED DESCRIPTION

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings.

An embodiment is shown in FIG. 1. The crawler unit comprises of multiple, but preferably two, modules mechanically connected by hydraulic cylinders. Each module has a clamp unit, with at least a single one of these module clamp units comprising a set of driven rollers or tracks capable of propelling the unit along the axis of the umbilical, riser, or tube.

The front module has three clamping units, although could be in excess of this, which incorporate at least a single driven set of rollers or tracks. Each clamping unit has a pair of rollers which are sufficiently spaced to give moment support from the umbilical, riser or pipe (600 mm separation shown on the embodiment in FIG. 2). A degree of moment support on the module is required, as it is intended that the module can support/hold the crawler unit onto the umbilical, riser, or pipe without the rear or any other additional modules providing additional support. The moment support helps keep both modules concentric with the umbilical, riser or pipe while the other is open.

When clamped onto the umbilical, riser or pipe the crawler unit can be driven along using the driven rollers. In embodiment shown all 3 roller set are driven, with each pair mechanically linked (by chain, shaft, or belt). The rollers themselves can have a concave surface to suite a range of diameters, which could be changed out to suit, which both helps to reduce contact pressure and holds umbilical, riser or tube more securely.

The clamping units of each module can open up to clear an item of larger diameter than the umbilical, riser or tube, such as strakes or buoyancy. FIG. 3 shows various positions of the clamping and centralising units for each module.

The centralising units (or guides) are required to keep the umbilical, riser, or pipeline concentric with the module as the clamping units close around, and without them the umbilical, riser, or tube risks being missed by the clamping wheels.

When the crawler unit is only supported by a single module, although a degree of moment support is provided, it is likely that the umbilical, riser, or pipe, although remaining contained by the centralising fingers of the module, would not be concentric prior to closing of its clamping units. In addition it aids in initial attachment by self-centralising when the crawler unit is first placed around the umbilical, riser or tube. A segment of the centralising units is able to open up, to both allow initial placement on the umbilical, riser or pipe, and to allow the unit to pass mooring cables, the detail of which shall be described further on in an operational sequence.

The centralising fingers of the preferred embodiment are part of the module clamping units, and so do not require additional actuation, although alternative embodiments could use a centralising system which is separate from the clamping mechanism. The fingers are mounted to a parallel link which is always parallel to the umbilical, riser or pipe as shown in FIG. 2, with the clamping wheels a set distance closer to the umbilical, riser or tube, so giving same amount of clearance between finger and umbilical, riser or tube regardless of diameter closed around. The centralising fingers themselves have an overlapping arrangement to form an aperture surrounding the umbilical, riser or tube.

The set of centralising fingers shown on the preferred embodiment are intended to be used for the full crawler unit diameter range; however, these are capable of being swapped out for a set suiting a specific diameter, or for alternative designs such as a set incorporating roller elements.

The rear module is used to provide a second clamp for hand-over-hand prolusion, for rotation about the umbilical, riser or tube axis, and as a light contact support while traversing along the umbilical, riser or tube using the driven rollers. The rear module driven clamping rollers are orientated to rotate the crawler unit about the umbilical, riser or tube axis. The non-driven caster rollers of each clamping mechanism are supported by a spring stack. When first closed, there is a gap between the rotational drive wheel and surface of umbilical, riser or tube, with only the caster wheel in contact, acting as a light support for keeping the rear module concentric with the umbilical, riser, or tube.

When rotation is required, the clamp mechanism is further closed, compressing the caster spring stack until the rotational drive wheel is clamped onto the umbilical, riser, or tube. The caster axis runs through the centre of the caster wheel, and will rotate though 90 degree as the crawler unit is first rotated. With rotational motors in hold, the rear module acts a moment supporting clamp for hand-over-hand propulsion.

The preferred embodiment of the crawler unit uses an on-board accumulator, or multiple with various pressure ranges, to supply a constant push force to a number of the clamp cylinders. Of the three clamp cylinders on a module, two of them are used to supply a constant push force (Supplied from accumulator), while the other is used to control the position, used to keep the umbilical, riser or tube central within the module. At least a single clamp arm (which would be one used to control position) would have positional feed back to the PLC from a sensor such as a liner transducer.

The preferred embodiment of the crawler unit uses an on-board HPU in conjunction with hydraulic motors and cylinders for reliability, and to enable power to be supplied electrically to simplify the umbilical, rather than having to supply hydraulic power via hoses. Supplying hydraulic power via an umbilical could however be an embodiment of the crawler unit, and may even be preferred when only short umbilical lengths are required, as it removes need for a sub-sea or marinised HPU. An on-board power supply such as a battery could also be used to remove the need to supply power through an umbilical.

The preferred embodiment for controlling the crawler unit is by use of an on-board PLC, with communication with a surface user control console. The PLC shall use inputs from both on-board sensors and surface control console inputs to control hydraulic manifolds and other on-board systems. Communication between the PLC and any other on-board systems such as cameras or a sensor/inspection module being carried by the crawler unit, shall preferably be done via a fibre optic core within a combined power and control umbilical.

The embodiment could also have incorporated a set of subsea thrusters to enable the crawler unit to position itself onto the umbilical, riser or tube without the need for diver or ROV intervention. The crawler unit would be first deployed into the water, and would then swim to, and orientate itself with, the umbilical, riser or tube. Further to this, the embodiment could also feature adjustable ballast, which would allow the unit to adjust the amount, and position of its centre of buoyancy. This could be used to help maintain a desired crawler unit orientation when submerged.

Operational Sequence

-   1) The front module rollers are used to propel the crawler unit     along the umbilical, riser, or tube until reaching an item such as a     clamp on buoyancy or strake, or simply a section of umbilical,     riser, or tube which the rollers cannot be driven over, as shown in     FIG. 4. The rear module caster rollers are lightly clamped onto the     surface of the umbilical, riser, or tube to support the rear of the     climber unit. -   2) The rear module clamping units are fully closed, with caster     roller spring stack compressed, and rotational rollers clamped onto     umbilical, riser or tube. The front module clamp rollers, including     the centralising fingers, are then fully opened to allow passage of     an item.     -   At this point the crawling unit would be rotated to align gap         with the mooring rope if required. Note also that should an item         or object extend outside the maximum module aperture diameter,         such as a buoyancy mooring line, then the centralising fingers         will also need to be opened as shown in FIG. 5. -   3) The walking cylinders are extended to move front module in     direction of travel, positioning front module rollers over or beyond     item being passed. The front module rollers are then clamped onto     the surface of the item, umbilical, riser or tube as shown in     FIG. 6. The front module rollers being driven are normally in hold,     so preventing crawler unit from freely traversing. -   4) The rear module clamps are partially released, removing the     rotational rollers from the surface of the umbilical, riser, or     tube, but keeping the caster rollers in contact to give support to     the rear module. The walking cylinders are then retracted, moving     the rear module either nearer, over or beyond the item as shown in     FIG. 7. Note that when the rear module is being taken past an item     the rear clamps would need to be fully opened rather than serving as     a support. In instances of the rear or front clamp being fully     opened, then the other clamp would be providing moment support to     try and keep the modules concentric to the umbilical, riser or tube.     Should the umbilical, riser or tube lose concentricity with either     module, the centralising fingers will return the module to being     concentric as the clamps are closed. -   5) The rear module clamping units are again fully closed as they     were in step 2, and the hand-over-hand propulsion process is     repeated until the item is fully cleared, as shown in FIG. 8. -   6) Once fully clear of the item or obstacle, and front module driven     roller engaged onto a section of umbilical, riser or tube which can     be driven across, the rear module caster rollers are positioned to     provide a light support, with rotational rollers clear from surface     of umbilical, riser or tube, as shown in FIG. 9.

A further embodiment of the present invention relates to a subsea, bi-directional tool that is able to clean and inspect the outside diameter of risers, umbilical's, flowlines, pipelines, mooring lines, ropes, cables and subsea conduit structures. Further, the tool could be used as a cargo lift to transport equipment to the ocean floor or from the ocean floor to the surface.

The tool is controlled and operated by a topside operative via a power and/or control umbilical.

The tool may carry a hydraulic power unit (HPU) or it may be remotely located.

The tool has the ability to rapidly traverse structures by using drive wheels, rollers or tracks.

The tool has the ability to step over obstacles, for example, anti-VIV strakes, mooring rope clamps, pipe flanges or buoyancy modules, by combining the actions of its driven wheels, its ability to lock the rotational aspect of its driven wheels, the ability to withdraw its driven wheels from the structure, and by extending or retracting its linear stepping actuators.

The tool can swim and attach itself to subsea conduits.

The tool can swim along and rotate about the axis of subsea conduits by retracting all wheels and using thrusters in combination with proximity sensors to remain concentric to the structure being traversed. (Note: the thrusters and sensors mentioned are not shown in the following figures).

The tool is also able to rotationally trim itself through the use of front and rear steering.

The tool in FIG. 10 comprises front and rear modules. The modules are interconnected by three double acting hydraulic stepping actuators—actuators are used to step/span over obstacles. Each module is made up of two distinct hinged halves—in the style of a clamshell—this enables the tool to open and close around the umbilical or conduit. The halves of each module are moved towards and away from one another by one or more double acting hydraulic actuators. When the two halves are closed a gap remains, this allows the tool to pass mooring ropes without detaching its drive mechanism or itself from the structure it is traversing.

The front and rear modules of the tool each have six wheels, split into three groups of two wheels, each group being arranged at 120° radial intervals. In this embodiment, the tyres on the wheels are formed with a concave radii to suit the outside diameter profile of the structure being traversed. The double, in-line wheel arrangement at each end of the tool is designed to give moment support when the wheels at one end of the tool are fully withdrawn, for example, when stepping over an obstacle. The wheel arrangement of the tool in this preferred embodiment, as shown in FIG. 1, can accommodate nominal structure diameters between 4″ OD and 24″ OD. Note: the clearance bore (I.D.) of the tool is 800 mm (31.5″) and the basic design principles of the tool can be scaled.

FIG. 11 shows an end view of the tool. Here, the tool is shown attached to a 12″ OD riser—the gap for passing a mooring rope or other slender off-take is clearly shown, as are the two halves of the clamshell arrangement—halves A and B. The double acting clamshell hydraulic actuator(s) is used to open and close the clamshell. A steering gear and actuator mechanism are provided on each of the two modules, with the steering gear allowing a limited amount of rotational trim to be applied as the tool traverses—thus, irrespective of the direction of travel of the tool, full rotational tool trim can be maintained—in all respects, the tool is fully bi-directional.

Tool Operation

The tool can be attached onto the structure to be cleaned or inspected in a number of ways. It can be manually attached by either divers at or near the surface or subsea, it can be loaded at or above the splash zone/surface by operatives in a tender, or the tool can also swim under its own power to the structure.

To attach, all wheel carriers are fully retracted to ensure the maximum tool clearance bore available, and the clamshell is opened. FIG. 12 shows both modules fully open and all wheel carriers fully retracted. (Note: In FIG. 12 a set of wheels on each module has been omitted for clarity).

The tool maneuvers to encircle the structure and the clamshell closes. Tool centralising occurs in one of two ways: by centralising fingers (shown in FIG. 13), two of which are connected to each wheel carrier, each wheel carrier covering a 120° segment—three segments per module covering 360°. FIG. 13 shows the wheel carriers closing, that is, extending towards the structure they will clamp on to—the centralising fingers move simultaneously. The fingers are designed to overlap and clear one another, thus they are able to close down to less than 4″ OD. Another method of centralising the tool is the use of proximity sensors arranged around the perimeter of the tool.

As the wheel carriers begin to move towards the structure (which move at the same rate, and are at the same extension), the position of the umbilical or conduit from each wheel carrier is measured, which also allows the control system to operate thrusters to keep the umbilical or conduit concentric as the wheel carriers close on it.

FIG. 10 shows the tool correctly loaded onto the structure. The tool can now undertake its intended operation, whether that be cleaning, inspection or transportation (Note: for clarity, no cleaning tools, inspection tools, transportation securing devices, centralising fingers, umbilical or HPU are shown in FIG. 10).

The tool is driven along the structure, steering and correcting its rotational attitude via operator input or by a control system making constant adjustment to the trim, with a sensor such as a gyrocompass used to measure relative rotational position. Where an obstacle is observed approaching, the steering gear on the tool is used to align the mooring rope gap. The diameter of an approaching rope can be measured to ensure safe passage through the mooring rope gap. Through appropriate sensing and detection, should the tool or operator determine that it is not possible to safely pass due to obstacle size or geometry, then the tool can revert to swimming mode.

In swimming mode the tool will retract all of its wheels. FIG. 14 shows the tool in this orientation, the tool can use thrusters to move over/past the obstacle as long as the tool ID provides sufficient clearance.

As the tool traverses the structure, the steering gear has the ability to induce continuous corrections to the rotational attitude of the tool—this prevents the tool winding its umbilical around the structure and subsequently stalling. However, it may be desirable to impose deliberate tool rotation to pre-wind the umbilical around the structure—this may be useful where, for example, the tool is required to traverse anti-VIV devices that contains helical strakes or fins. The pre-wind would be imposed in a direction opposite to that of the strake helix, such that, the two should cancel out one another, post obstacle traversal. Further, half the required pre-winding could be imposed before the obstacle and half removed post obstacle. Finally, full helical correction could be made after the traversal of the obstacle. Should umbilical winding be so large as to stop the tool traversing, or there is insufficient rotation rate from trim to unwind, then the tool can release all of its wheels and rotate itself around the structure using thrusters to unwind it.

It is intended that the tool's centre of buoyancy will be in the same position as its centre of gravity, so that there is little or no moment applied to the umbilical, riser or tube when clamped using a single module. If this was not the case then the self-weight and buoyancy forces could act to rotate the tool. This reduces the forces the wheel carrier actuator shafts and bodies are exposed to.

Where the tool meets an obstacle it has the ability to step over it. However, the tool does not necessarily need to use its stepping actuators (FIG. 10) for this task, as demonstrated in FIGS. 15 to 18.

-   -   The tool drives up to an obstacle, retracts the wheel carriers         of the module nearest the obstacle (leading), whilst still being         supported by the wheel carriers located on the other module         (trailing).     -   The remaining set of wheels still in contact with the structure         (trailing) drive the retracted wheels (leading) over the         obstacle (Shown in FIG. 16).     -   The leading module re-clamps against the structure having         cleared the obstacle, and the trailing module wheels are opened         (Shown in FIG. 17).     -   The leading module wheels move the trailing wheels clear of the         obstacle and are re-clamped against the structure. The tool can         now continue on its way (Shown in FIG. 18).

FIGS. 15 to 18 show the tool passing a buoyancy attachment type obstacle.

The extending actuators are included in the design to allow the tool to step over complex geometry, for example, where multiple obstacles occur in close proximity to one another FIGS. 19 to 24. Further, the tool also has the ability to withdraw front and rear wheel carriers/systems completely, and simply swim over an obstacle while remaining concentric with the umbilical, riser or tube it is traversing.

The general arrangement of a riser and umbilical crawler used for delivering flexible inspection tools formed according to an alternative aspect is shown in FIG. 25.

The basic crawler unit is not able to pass over objects such as strakes or buoyancy, however would cope with limited diameter and ovality changes. The unit is hydraulically driven, and uses cylinders backed by a hydraulic accumulator to apply a constant clamp force to the umbilical. The umbilical is contacted by conforming polyurethane concave rollers, two of which are driven, to reduce contact pressure.

The unit shown in FIGS. 25 and 26 can accommodate an umbilical diameter range from 14″ to 8″, however a change out of the rollers (either to a larger or smaller diameter) would allow the crawler to be used with a different riser or umbilical diameter range.

FIG. 27A shows the crawler unit open and positioned around a 14 inch diameter umbilical. FIG. 27B shows the unit closed around the umbilical. FIG. 27C shows the unit closed around an 8 inch umbilical.

Before being placed around a riser or umbilical, the central roller set is positioned to suit the intended diameter, which is done by removing a couple of pins, positioning the central roller set, and re-pinning to the crawler frame.

The crawler unit may allow inspection and cleaning tools to be deployed to positions where space limitations prohibit an ROV, such as within a tightly packed group of risers or umbilicals as shown in FIG. 28. Crawler unit could be attached directly to closely packed riser, or further along Riser/Umbilical were spacing has sufficiently increased to allow attachment by an ROV.

While designed to suit a range of diameters, the prototype Crawler unit may not be suited to diameters smaller than 8″, with Risers or Umbilical's of smaller diameter potentially requiring an alternative unit. DNV recommended practice (DNV-RP-F203) is for Risers to have a minimum spacing of 2×OD between outers surfaces, as shown in FIG. 28 for a 14″ diameter. In some embodiments the crawler can be positioned between 14″ Risers, it takes a spacing of at least 3×OD for the Crawler to be positioned within a collection of 8″ Risers. While 2×OD is given as the minimum spacing, this is usually greater for smaller diameter Risers, as spacing is dictated by that of their hang off collars. The crawler unit requires a minimum spacing of 600 mm between outside faces to pass between a collection of risers or umbilicals.

While the crawler unit may have limited access to tightly packed small diameter (<8″) Risers as indicated in FIG. 28, it would be better suited to deployment of inspection and cleaning tools than a free flying ROV, which have far greater access limitations within a group of tightly packed risers or umbilical's (the body of ROV+inspection tool would sit within a much larger space envelope than that highlighted by red circle in FIG. 28).

The crawler unit may be configured to have some/all of the following features:

-   -   100 m depth rating.     -   Hydraulic actuation and drive motors.     -   Positive buoyancy.     -   Weight—˜130 kg.     -   Height—700 mm. (1600 mm including buoyancy & brushes)     -   Optional cameras, lighting, and sensors.     -   PC controlled via optical Ethernet connection.     -   Flexible inspection tool/net in air load—+75 kg.

The crawler unit could be attached to the riser or umbilical in a number of ways. The crawler unit could be deployed by first lowering it into the water using either an existing crane or a dedicated over boarding system such as an A-frame. The crawler unit sits upright when in water, with its centre of buoyancy located both centrally and above its centre of gravity. Once in the water the unit would be maneuvered around the riser or umbilical by either divers, an ROV (although one of the key advantages of the Crawler is to negate the use of free flying work class ROV's), or possibly even by its own thrusters (Self swim). The crawler unit could either be closed around the riser by divers using local control for safety, or remotely from the controlling PC. Environmental conditions may be too severe to allow the crawler unit to be attached at the water surface, with risk to personnel or ROV being ‘slammed’ against riser, umbilical, FPSO or Jacket structure. The crawler unit could be deployed onto the riser or umbilical by an ROV below the surface of the water, in a similar manner to how a number of inspection tools are currently deployed, and could be recovered directly using a lift line rather than additional ROV manipulation.

The crawler unit could also be made negatively (or at least near neutrally) buoyant, which would allow divers to attach the crawler below the surface of the water rather than use an ROV. The crawler unit could also be directly deployed onto the riser or umbilical from above the water.

Assuming the crawler has been lowered into the water from the deck of an FPSO or Jacket, the line used to deploy the unit could be kept attached for retrieval, or as a fall restrictor if being operated above the waterline.

The control valves could be arranged to suit how the crawler is to be deployed. If for example the unit was to traverse below the surface of the water, then the clamps could be made to open following loss in power or communication, allowing the crawler to freely float to the surface. This would not be suitable if the crawler was being driven up from the water line, where the unit would remain clamped with rollers locked following loss in power or communication. A normal ‘release’ state in this situation would only be acceptable if the crawler had a safety or lift line (fall restrictor) from above. It could be possible that following a power or communication failure that the rollers remain clamped, but the motors are throttled, which would give the crawler a steady decent if above water, or allow it to float to the surface if below it.

Following a failed subsea surface retrieval, an ROV or Diver could be used to operate a manual valve to release and open the rollers, allowing the crawler to freely float or be lifted to the surface.

It may be possible to integrate an existing inspection tool of choice into the crawler.

Inspection tools may be attached to the upper side of the crawler, with cleaning equipment located on the underside, so inspection elements do not have to work through thickness of accumulated marine fouling. An inspection tool attached to the crawler is shown in FIG. 29.

A sensor package could be a simple fixed attachment suited to a particular riser or umbilical diameter

The sensor mounting could be slightly loaded against the umbilical so that it is always a set distance from the surface

It may be of benefit to have ability to rotate the sensor about the axis of the riser or umbilical, and if so the inspection tool mounting could enable limited rotation of the tool (/+60 degree, or a full+/−180 mounting could be investigated).

The inspection tool may be connected to the crawler unit subsea electronics pod, which provides it with an Ethernet connection to a surface PC.

The riser and umbilical crawler subsea electrical pod may contain the units controller (for example a PLC), which is used to drive valves on the hydraulic manifold, as well as connect to additional I/O such as auxiliary systems and sensors. Although partially dependent on umbilical crawler depth requirement, it is likely that the electronics pod will be oil filled and pressure compensated.

The on-board control unit may be connected to a surface PC, with the surface PC used as an input to the on-board control unit. The surface PC would be connected to the control unit through a fibre via an Ethernet to Fibre convertor. On-board subsea IP cameras could also be used to relay video to the surface PC if required, allowing the operator to perform visual inspection, and to monitor the crawler unit as it moves and/or cleans along the Riser or Umbilical.

Sensor and tool packages carried by the crawler may be connected to the subsea electronics pod, with data relayed to a surface PC via same fibre optic data line used for control and any IP cameras.

FIG. 30 shows proposed system overview.

The same PC used to read and record data from the inspection tool could also be used to control the crawler, with interface software provided.

Additional analogue or digital I/O which could be connected to the on-board control unit could include:

-   -   Pressure sensors.     -   Rotatory encoder; for measuring speed and distance travelled         along the Riser or Umbilical.     -   Linear transducer; for giving cylinder positions.     -   Leak detection; if not oil filled.     -   Oil compensator position or min level warning.

In one embodiment the following are used:

-   -   4× Pressure transducers; for accumulator (×2), return, and         supply pressure.     -   1× Rotatory encoder; for measuring speed and distance traveled         along the umbilical.

In some embodiments the crawler requires hydraulic power to drive motors and cylinders, which will be supplied from a remote surface HPU (other embodiments may have on-board HPU). As some units are only required to travel to relatively shallow depths of between 50-100 m, and as it has a low power requirement, then it would be feasible to supply hydraulic power via a neutrally buoyant hose, such as those used to drive diver operated equipment.

In addition to hydraulic power, the crawler may be supplied with a 28 VDC electrical supply and fibre control core. It is envisaged that any tool or sensor package to be carried would be supplied via common electrical cores supplying the crawler unit, with the tool or sensor package being connected to the unit's subsea electrical pod.

Rather than using an expensive bespoke umbilical, the prototype unit will use a collection of individual cores to make up its umbilical. The cores may be kept together in a spiral cable wrap or similar cable management/tidy cover.

The fibres and electrical cores may terminate into small housings onto dry-mate connectors, and hydraulic lines would terminate with quick-connects, allowing the umbilical to be quickly detached (or replaced) from the crawler unit. The quick connects may connect directly to the control manifold, while the electrical and fibre dry-mate connectors would connect to the electronics pod.

In many cases, before inspection by various sensor packages, the riser or umbilical must be relatively free of marine fouling, Embodiments of the present invention may comprise a riser and umbilical cleaning module which can be carried by/integrated into the crawler unit.

For example, the brush cleaning attachments shown in FIGS. 31 and 32 would allow for 360° continual cleaning, allowing the crawler to progress at a constant speed along the umbilical. Cleaning is done using three hydraulically driven brush heads pressed against the surface of the umbilical. The cleaning brushes would be suited to a particular diameter, or at best a limited diameter range, so would need to be changed out to suit diameter to be cleaned. A scrapper could possibly be attached ahead of the brushes, just off the surface of the umbilical, to remove the bulk of any dense marine fouling.

In this embodiment the brush heads are generally cylindrical but taper inwards from each side towards their centre so that they fit onto a generally cylindrical target.

Allowing the deployment of inspection and cleaning tools above, below, and within the splash zone. It would require a combination of ROV's or divers, and personnel hanging from ropes to deploy to same locations. The unit could be attached at any point along the riser or umbilical, and traverse to position above, below, or within splash zone.

While ROV's or divers may be capable of deploying inspection or cleaning tools at a distance below the water line, surface waves may make it difficult or impossible to position and hold a tool at or near its surface. The crawler unit could be attached either above or below the water line if surface attachment is not possible, while being able to move into and hold itself within the splash zone. This would remove need for divers or expensive ROV's to operate near the surface where environmental conditions may be too severe (risk to personnel or equipment being ‘slammed’ into Riser, Umbilical, FPSO, or Jacket structure).

The crawler unit may use the riser/umbilical to attach and position itself, giving greater positioning and attachment security than a free flying ROV, and so allowing a larger environmental operating window.

The crawler unit may combine riser/umbilical cleaning (often required before inspection) and inspection into a single tool deployment and operation. Many present systems have to use an ROV with a cleaning tool before redeploying with an inspection tool. The present invention removes the need to tie up high value work class ROV's and their pilots, at most being required for initial attachment and removal, or possibly not at all if attached by personnel or self-swim ability.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment shown and that various changes and modifications can be affected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. 

What is claimed: 1) A dual-mode crawler unit for traversing a generally tubular target, the unit comprising two or more traversing modules which can effect a hand-over-hand action along the target and also a driven action along the target, the units being connected to each other by one or more linear actuators. 2) A unit as claimed in any claim 1, in which the modules comprise drive means selected from: rollers, tracks, wheels, thrusters, rolling support means, bristle drive or the like for effecting a driven action along the target. 3) A unit as claimed in claim 1, in which the modules comprise clamps for effecting a hand-over-hand action. 4) A unit as claimed in claim 3, in which the clamps are capable of moving toward and away from each other along the target. 5) A unit as claimed in claim 1, in which there are two sets of driven rollers, tracks or wheels separated by a linear actuator, and in which each set of driven rollers or tracks is capable of supporting and propelling the unit/tool along the target without the other being in contact with the target. 6) A unit as claimed in claim 1, comprising a roller, track or wheel capable of rotating the unit about the tubular target. 7) A unit or tool as claimed in claim 2, in which the drive means are movable between a retracted position and an engaged position. 8) A unit as claimed in claim 1, including thrusters for traversing the target and/or for keeping the unit concentric with the target during movement. 9) A unit as claimed in claim 1, including sensors for keeping the unit concentric with the target. 10) A unit as claimed in claim 1, including capability to adjust clockwise or anticlockwise rotation bias. 11) A unit as claimed in claim 1, which incorporates a sensor for giving its rotational position, either absolute, or relative to a datum. 12) A unit as claimed in claim 1, where a control system is used to automatically adjust clockwise or anticlockwise bias to maintain a desired rotational position or path on the target. 13) A unit as claimed in claim 1, where the modules include clamps for effecting hand-over-hand action comprise clamps and the clamps include a set of overlapping fingers forming an aperture, which retain the target when the clamps are opened, and centralize the target as the clamps are closed. 14) A unit as claimed in claim 1, including an on-board electrically driven HPU. 15) A unit as claimed in claim 1, including a module for cleaning the target. 16) A unit or tool as claimed in claim 15, in which the module cleans the target by scraping and/or rotating brushes and/or water jetting. 17) A unit or tool as claimed in claim 1, including a sensor or inspection module. 18) A unit as claimed in claim 1, including a set of subsea thrusters to enable the unit to swim, so to position itself around the target when in water. 19) A subsea bi-directional crawler unit for traversing a generally tubular target, in which the unit includes capability to monitor and correct rotational position, the unit comprising a sensor for providing absolute or relative rotation to a target and the ability to actively rotate the unit. 20) A crawler unit comprising a frame with a generally central roller set, a pair of lateral roller sets being provided on or by each side of the frame and being movable from an open position in which the frame can be positioned on a tubular target with the central roller set engaged, and a closed position in which the lateral roller sets are closed around the target and engage thereon. 